linux-kernel - Re: [PATCH v3 6/7] iommu/mediatek: Use writel for TLB range invalidation

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Message-ID: <c87e2a9c-5ed3-e44c-3b17-067db173eae9@arm.com>
Date:   Mon, 14 Oct 2019 15:04:42 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>
Cc:     Evan Green <evgreen@...omium.org>, Tomasz Figa <tfiga@...gle.com>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>, anan.sun@...iatek.com,
        cui.zhang@...iatek.com, chao.hao@...iatek.com,
        edison.hsieh@...iatek.com
Subject: Re: [PATCH v3 6/7] iommu/mediatek: Use writel for TLB range
 invalidation

On 14/10/2019 07:38, Yong Wu wrote:
> Use writel for the register F_MMU_INV_RANGE which is for triggering the
> HW work. We expect all the setting(iova_start/iova_end...) have already
> been finished before F_MMU_INV_RANGE.

For Arm CPUs, these registers should be mapped as Device memory, 
therefore the same-peripheral rule should implicitly enforce that the 
accesses are made in program order, hence you're unlikely to have seen a 
problem in reality. However, the logical reasoning for the change seems 
valid in general, so I'd argue that it's still worth making if only for 
the sake of good practice:

Acked-by: Robin Murphy <robin.murphy@....com>

> Signed-off-by: Anan.Sun <anan.sun@...iatek.com>
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
>   drivers/iommu/mtk_iommu.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index dbbacc3..d285457 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -187,8 +187,7 @@ static void mtk_iommu_tlb_flush_range_sync(unsigned long iova, size_t size,
>   		writel_relaxed(iova, data->base + REG_MMU_INVLD_START_A);
>   		writel_relaxed(iova + size - 1,
>   			       data->base + REG_MMU_INVLD_END_A);
> -		writel_relaxed(F_MMU_INV_RANGE,
> -			       data->base + REG_MMU_INVALIDATE);
> +		writel(F_MMU_INV_RANGE, data->base + REG_MMU_INVALIDATE);
>   
>   		/* tlb sync */
>   		ret = readl_poll_timeout_atomic(data->base + REG_MMU_CPE_DONE,
>